The present study examined the effects of acute administrations of phenytoin on the lever pressing of rats maintained under fixed-ratio, fixed-interval, and interresponse-time-greater-than-T schedules of food delivery. The drug typically produced dose-dependent decreases in response rates under fixed-ratio and fixed-interval schedules, while response rates under the interresponse-time-greater-than-T schedule were affected little by the drug. These findings indicate that phenytoin effects on schedulecontrolled responding differ from those of other anticonvulsants.